US20020183846A1 - Spinal implant - Google Patents

Abstract

An implant is disclosed for use in spinal stabilization. In one preferred embodiment, the implant is described as including a hollow, cylindrical body having external threading and a plurality of openings formed radially through the body in communication with the body interior. The holes are positioned to chip bone into the implant as the implant is rotated.

Description

I. CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a divisional application of Ser. No. 07/702,351 which is a continuation-in-part of U.S. Ser. No. 07/405,564 which is a continuation-in-part application claiming priority to commonly assigned U.S. patent application Ser. No. 07/376,657, filed Jul. 6, 1989, entitled “Spinal Prosthesis” and naming the same inventors as the present invention.[0001]
II. BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0002]
• This invention pertains to surgical procedures for stabilizing the spine. More particularly, this invention pertains to a novel implant for use in such a procedure.[0003]
• 2. Description of the Prior Art[0004]
• Chronic low back pain is one of the most common and perplexing problems facing the field of orthopedic surgery. In addition to patient discomfort, chronic low back pain has severe adverse societal impacts including lost income, possible chronic dependence on drugs, alcohol and public relief programs.[0005]
• In many cases, low back pain can be avoided by preventing relative motion between spinal vertebrae (commonly referred to as intervertebral stabilization). To abate low back pain, stabilization is directed to stabilizing contiguous vertebrae in the lumbar region of the spine.[0006]
• Surgical techniques are known for use in spinal stabilization. Surgical techniques seek to rigidly join vertebrae which are separated by a degenerated disk. Ideally, the surgery effectively replaces the vertebra-disk-vertebra combination with a single rigid vertebra. Various surgical techniques have developed which attempt to approach or approximate this ideal.[0007]
• One technique known in the art is to partially remove a degenerated disk and to insert a bone graft into the void formed by the removed disk. Other techniques involve the use of an implant which, acting alone or in combination with bone fragments, replace the use of bone grafts. An example of such implant is shown in U.S. Pat. No. 4,501,269 to Bagby dated Feb. 26, 1985. In Bagby, a large, cylindrical basket is driven into a hole formed between bones which are to be joined. The basket is hollow and is filled with bone fragments which are produced during a boring step. Bone-to-bone fusion is achieved through and about the basket. In Bagby, the hole for the Basket is slightly smaller than the diameter of the basket. This structure results in the spreading of the opposing bone segments upon insertion of the basket. This results in taughtness, which provides initial stabilization. Eventual fusion of the opposing bone segments results from bone growth through the basket.[0008]
• Prostheses such as that shown in U.S. Pat. No. 4,501,269 are promising. However, improved implant design is necessary to enhance patient safety and the probability of a satisfactory recovery.[0009]
III. SUMMARY OF THE INVENTION
• According to a preferred embodiment of the present invention, an implant is disclosed for insertion into a body formed between opposing vertebrae of an animal's spine. The implant includes a rigid body having a leading end and a trailing end spaced apart along a longitudinal axis of the body. The body has exposed threads which are disposed between the leading and trailing ends. The threads are selected to engage vertebra material and draw the body along the direction of the axis upon rotation of the body about the axis. The body defines a chamber which is exposed through the body by a plurality of radially extending openings. The chamber may be filled with bone fragments which can fuse with the vertebra bone material through the openings. In one embodiment, a reinforcing rib is provided within the body.[0010]
• In an alternative embodiment of the invention disclosed herein, a generally oval-shaped implant is disclosed which is hammered into an elongated bore between two opposing vertebrae. The oval-shaped implant has enhanced surface area contact between the vertebrae and provides greater integrity against rotational motion between opposing vertebrae.[0011]
IV. BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective exploded of view of an implant according to a preferred embodiment of the present invention;[0012]
• FIG. 2 is a side elevation view of a body portion of the implant of FIG. 1;[0013]
• FIG. 2A is a side elevation view of an alternative embodiment of a body portion of an implant according to the present invention;[0014]
• FIG. 3 is an end view taken in elevation of the trailing end of the body portion of FIG. 2 taken along line[0015]3-3 of FIG. 2;
• FIG. 3A is the same view as FIG. 3 showing an alternative embodiment;[0016]
• FIG. 4 is a view taken along lines[0017]4-4 of FIG. 2;
• FIG. 4A is the same view as FIG. 4 showing an alternative embodiment;[0018]
• FIG. 5 is a view taken along line[0019]5-5 of FIG. 2;
• FIG. 6 is a view taken along lines[0020]6-6 of FIG. 3;
• FIG. 7 is an enlarged view, taken in section, of the threads of the body of FIG. 2 adjacent the trailing end;[0021]
• FIG. 7A is a view, taken in section, of the threads of the body portion of FIG. 2 adjacent a leading end of the body;[0022]
• FIG. 8 is a side sectional view of a leading end cap of the implant of FIG. 1;[0023]
• FIG. 9 is an inside end elevation view of the end cap of FIG. 8 taken along line[0024]9-9 of FIG. 8;
• FIG. 10 is a side sectional view of a trailing end cap of the implant of FIG. 1;[0025]
• FIG. 11 is an end elevation view of the end cap of FIG. 10 taken along line[0026]11-11 of FIG. 10;
• FIG. 12 is a top plan view showing insertion of a single implant of FIG. 1 into an intervertebral space;[0027]
• FIG. 12A is a view taken along lines[0028]12A-12A of FIG. 12;
• FIG. 13 is a top plan view showing an alternative embodiment of the present invention in place in a vertebra;[0029]
• FIG. 13A is a view taken along[0030]lines13A-13A of FIG. 13;
• FIG. 14 is a perspective view of an alternative embodiment of the present invention showing an implant body leading end, side and top;[0031]
• FIG. 15 is a perspective view of the body of FIG. 14 showing a trailing end, side and top;[0032]
• FIG. 16 is a top plan view of the embodiment of FIGS. 14 and 15;[0033]
• FIG. 17 is a side sectional view taken along lines[0034]17-17 of FIG. 16;
• FIG. 18 is a side elevation view of a trailing end cap for use with the embodiment of FIGS. 14 and 15;[0035]
• FIG. 19 is an end view taken in elevation of the end cap of FIG. 18;[0036]
• FIG. 20 is an elevation view a trailing end of the embodiment of FIGS. 14 and 15;[0037]
• FIG. 21 is an elevation view of a leading end of the body of the embodiment of FIGS. 14 and 15;[0038]
• FIG. 22 is a side elevation view of the body portion of FIGS. 14 and 15;[0039]
• FIG. 23 is a top plan view of an assembled implant including body portion and end cap shown in place in a vertebra body;[0040]
• FIG. 24 is an anterior elevation view showing a bore drilling sequence prior to insertion of the implant as shown in FIG. 23;[0041]
• FIG. 25 is a view taken along lines[0042]25-25 of FIG. 23;
• FIG. 26 is a cross-sectional view taken along a longitudinal axis of an alternative embodiment of the present invention;[0043]
• FIG. 27 is a cross-sectional axial view of the embodiment of FIG. 26;[0044]
• FIG. 28 is a cross-sectional longitudinal view of an additional alternative embodiment of the present invention; and[0045]
• FIG. 29 is a cross-sectional axial view of the embodiment of FIG. 28.[0046]
V. DESCRIPTION OF THE PREFERRED EMBODIMENT
• A. General.[0047]
• Reference is now directed to FIGS. 1 and 12. FIG. 1 is an exploded perspective view of an implant according to a preferred embodiment of the present invention. The implant is shown generally at[0048]10. FIG. 12 shows theimplant10 inserted within abore102 formed in ahuman vertebra body100.
• For ease of description, the implant[0049]10 (as well as alternative embodiments of the invention) will be described for use in a human spine. Further, dimensions, when given, will be preferred dimensions for use in a specific spinal location of a particular class of humans—notably, the L-5 vertebra of a typical adult male. It will be appreciated that the present invention is intended for use in a wide variety of vertebra sizes and a wide variety of animal species. The dimensions of the implant10 (as well as the dimensions of the alternative embodiments) will vary necessarily with the size of the vertebra in which theimplant10 is to be used. However, making variations to the dimensions and sizes in order to accommodate differing sizes of vertebrae will be well within the skill of the art.
• B. First Preferred Embodiment.[0050]
• With reference now directed to FIGS.[0051]1-12, a first preferred embodiment of the present invention will now be described. Identical elements are numbered identically throughout.
• The[0052]implant10 includes a body12 (shown separately in FIGS.2,3-6) having a leadingend14 and a trailingend16 which are spaced apart along a longitudinal axis X-X of thebody12. The implant also includes aleading end cap18 and a trailing end cap20 (shown separately in FIGS.8-9 and FIGS.10-11, respectively).
• [0053]Body12 is integrally constructed from a rigid, biocompatible material. While any rigid, biocompatible material (such as a ceramic) could be used,body12 is preferably formed from titanium and/or its alloys. Titanium and/or its alloys is preferred since it is noncorrosive and fatigue resistant. Also, titanium is widely used in prosthetic devices and the material has a proven record of satisfactory performance.
• With best reference to FIGS.[0054]2-7 and7A, thebody12 includes a hollowcylindrical shell22 of predetermined diameter D₁(see FIG. 3). For reasons that will be later described D₁is selected to be about 0.5 inches.
• The[0055]shell22 surrounds and defines aninterior chamber24.Chamber24 has a diameter D₃of preferably about 0.384 inches.
• [0056]Threads26 and28 are formed on the exterior surface ofshell22 spirally wound aroundshell22 and integral therewith. While double threading is shown, single threading or multiple threading in excess of double threading could be applied.Threads26,28 are disposed and selected for thethreads26,28 to engage the bone material of opposing vertebrae and draw thebody12 in the direction of axis X-X upon rotation of thebody12 about axis X-X.
• In a preferred embodiment,[0057]body12 is self-tapping. Mainly, the threading26,28 (see FIG. 2) adjacent leadingend14 is tapered as shown by angle A₁(which is preferably about 15°, see FIG. 2). Away from thetapered end14, and adjacent the trailingend16, thethreads26,28 present flat, annular surfaces30 which are in alignment and parallel to shell22. Accordingly, the thread profile presents a generally bullet-shaped profile which is cylindrical along the majority of thebody12 and tapers inwardly toward axis X-X at theleading end14.
• The tapered portion of[0058]body12 preferably has a length L₁of about 0.198 inches. The overall length ofbody12, L₂, is preferably about 0.740 inches. (See FIG. 2).
• To assist in the self-tapping, the[0059]threads26,28 experience a change in profile from the leadingend14 to the trailingend16. At the leadingend14, the threads are sharp, as shown in FIG. 7A. When the taper portion ofbody12 is passed, thethreads26,28 assume a profile which is generally rectangular as shown in FIG. 7. For ease of discussion, the sharp portions ofthreads26,28 are numbered26a,28ain the drawings.
• The changing thread profiles are selected to assist in advancing the[0060]implant10 into an intervertebral space and to a hold theimplant10 securely in place when fully advanced. The sharp portion ofthreads26,28 (thread portions26a,28ashown in FIG. 7A) cut bone better and assist in advancing theimplant10. The generally rectangular thread profile (FIG. 7) has greater cross-sectional area and better opposes bone surfaces to hold theimplant10 in place.
• Preferred dimensions of the threading[0061]26,28 are shown in FIGS. 7 and 7A with a pitch, P, (distance between opposing threads) equaling about 0.10 inch for both the rectangular and sharp threading of FIGS. 7 and 7A. The bevel B1, of the sharp threading (FIG. 7A) is preferably about 57°. The bevel, B₂, of the rectangular thread portion (FIG. 7) is preferably about 5°. The height, H, of the rectangular thread is about 0.10 inches. This, together with the diameter D₁(see FIG. 3) of theshell22 results in overall diameter of thebody12 being about 0.6 inches. It will be appreciated that these dimensions as well as remaining dimensions given throughout this application are preferred dimensions and may be varied while retaining the structure and function of the present invention. The scope of the claims of the present invention is not intended to be limited by dimensions which are set forth only to illustrate a preferred embodiment.
• The[0062]body12 has a plurality ofholes32 formed radially through theshell22 andthreads26,28. Theholes32 provide communication betweeninterior chamber24 and an exterior of thebody12.
• The[0063]holes32 are identical and each is preferably about 0.125 inches in diameter. Shown best in FIG. 4, each of theholes32 includes a countersunkportion34 at the radially outer surface ofthreads26,28. Preferably, the countersunkportion34 has a diameter of about 0.155 inches.
• The countersunk[0064]portion34 creates cutting abeveled edge33 on therectangular threads26,28 in the location of theholes32. Thiscutting edge33 is best shown in FIG. 6. The cutting edges33 chip away bone as thebody12 is rotated. The bone chips will migrate through theholes32 intochamber24. As will be described, it is anticipated that this chipping action will enhance the bone-to-bone fusion sought with the present invention.
• In the region of the self-tapping[0065]sharp threads26a,28a(FIG. 7A), thethreads26a,28aare shown self-tapping in FIG. 5 to present self-tappingcutting edges36 set at a 90° cutting angle A₃. The cutting edges36 are shown spaced apart by an angle A₄of about 120°.
• In the preferred embodiment as shown, holes[0066]32 extend through thethreads26 and28. An alternative embodiment would have thethreads26 and28 spaced apart a distance greater than that shown in the present drawings, with theholes32 extending through theshell22 and not passing throughthreads26 and28. Such a design presents enhanced structural integrity since the moremassive threads26 and28 are not being broken. However, such an alternative design forgoes the anticipated benefits which may be attributed to the chipping action of the cutting edges33 of the threadsadjacent holes32.
• The number of[0067]holes32 in thebody12 as shown is twenty. This number may vary. The number is selected to be as many and as large as possible (to enhance bone fusion), while not compromising the strength of thebody12.
• As previously indicated, the[0068]body12 extends from a leadingend14 to a trailingend16. Leadingend14 has a circularaxial opening40 formed therethrough in communication withchamber24. Disposed inwardly from leadingend14 is an annular groove42 (see FIG. 6) provided to facilitate attachment of leadingend cap18 as will be described.
• Trailing[0069]end16 has an inwardly projectingflange44. opposing surfaces offlange44 define a centrally located hexagon-shapedaxial opening46.
• When the[0070]implant10 is in place in an intervertebral space, circularaxial opening40 and hexagonaxial opening46 are covered bycaps18 and20. Shown best in FIGS. 8 and 9, theleading end cap18 includes acylindrical hub portion50 and anannular flange52 extending fromhub portion50. Also extending fromhub portion50 on the side oppositeflange52 is a taperedcap portion54 which extends from alarge diameter55 and tapers inwardly to a smaller diameterterminal end56. An angle of taper A₅(FIG. 8) is preferably about 15° to correspond with the angle of taper A₁(FIG. 2) ofbody12. Thelarge diameter55 is preferably selected to equal the diameter ofbody12 at leadingend14.Flange52 is selected to be snap received intoannular groove42. So received,cap18 is permanently attached to theleading end14 coveringaxial opening40.
• Trailing end cover[0071]20 (FIGS. 10 and 11) includes anarcuate cap58 sized to coverend16 with aflat surface portion59 ofcap20abutting trailing end16. Six flexible retaining clips60 are provided centrally extending fromsurface59.Clips60 are sized to be snap received within hexagon-shapedopening46. Accordingly, the cooperation ofsurface59 and thebarbed portion61 ofclips60capture flange44 to thereby hold trailingend cap20 securely against trailingend16. For reasons that will be described, each ofcaps18 and20 are preferably formed from high-density polyethylene.
• C. Method of Use.[0072]
• Referring to FIGS. 12 and 12A, the method of use of the[0073]implant10 will now be described. In use of theimplant10, a surgeon forms abore102 through the intervertebral space in adisk114 separating two opposingvertebral bodies100 and100a. Thebore102 is sized to be as large as possible to removedisk material114 and to at least partially cut into opposing surfaces of the bone ofvertebra bodies100,100a. It will be appreciated that it is well within the skill of the art to form bores such asbore102.
• FIGS. 12 and 12A show a[0074]bore102 formed through a posterior approach through a spine. In a posterior approach, a surgeon approaches the vertebra through the back of the patient. Preferably, the axis of thebore102 is formed an angle with the anterior-posterior axis, A-P, of thevertebra body100,100a. As shown in the preferred surgical approach, the angle A₆between the A-P axis and the bore axis is about 10°.
• It is recognized that there are limits on the maximum size of a[0075]bore102 that can directly drilled in a vertebra body via a posterior approach. Limitations on the diameter of thebore102 include location of important nerves and blood vessels which can be damaged by excessively large bore drilling operations. The maximum size bore that can be cut will depend on the particular location of the spine, the species of the animal, age and sex. A common safe maximum for an adult male spine in the L-5 area would be a bore diameter of about 0.5 inches.
• For reasons that will be described, it is preferred that the bore diameter will be smaller than the diameter, D[0076]₁, ofbody shell22. Specifically, it is anticipated that a bore diameter of about 3 millimeters less than diameter D₁will be preferred. With such structure, thebody12 spreads apart opposing vertebrae upon insertion. By virtue of the spreading effect, the disk annulus becomes taught, thereby providing for the initial stabilization between the opposing vertebrae. (Those skilled in the art will recognize the annulus as being the fibrous outer circumferential portion of the disk). In the drawings, the implant is shown spreading apart the vertebrae and stretching the annulus. Eventual fusion of the opposing vertebrae results from bone growth throughbody12, as will be described.
• The[0077]implant10 is partially assembled withleading end cap18 snapped onto leadingend14. With trailingend cap20 removed, theimplant10 is partially placed withinbore102 with the tapered leadingend14 received withinbore102. An advancing tool (the tip of which is shown in FIG. 1) is provided having a hexagon-shapedtip200 complementarily sized to be received withinopening46. Thetip200 is inserted by the surgeon intoopening46. The surgeon then turns the tool and, hence, thebody12, in a clockwise direction (from the perspective of the surgeon). The turning action of thebody12 causes thesharp threads26a,28a(FIG. 7A) to cut into the bone of the opposingvertebrae bodies100,100ato advance thebody12 intobore102 to the fully inserted position shown in FIG. 12. Therectangular threads26,28 (FIG. 7) retain thebody12 in the desired axial position relative to bore102. Leadingend cap18 coveringaxial opening40 prevents disk material from migrating throughaxial opening40 intochamber24 during insertion ofimplant10 as well as during the patient's recovery phase.
• With the[0078]implant body12 fully inserted as shown in FIG. 12, the trailingend cap18 has not yet been installed. Accordingly,axial opening46 exposeschamber24 to the surgeon once thetool tip200 is removed. With opening46 still exposingchamber24, a surgeon can impact a graft medium202 (preferably bone chips) into chamber24 (see FIG. 12A). Any impacted bone chips will supplement bone chips that may migrate throughholes32 as a result of the cutting action of cuttingedges33 against the vertebra bone surfaces.
• With the graft medium fully applied to[0079]chamber24, the surgeon snapscap20 intohole46 to cover the trailingend16. FIGS. 12 and 12A show such a fully assembled and insertedimplant10. The surgeon can then close the patient through any suitable technique. With the completedimplant10 installed in the manner indicated, thebone graft202 withinchamber24 andopenings32 fuses together with the bone of the opposingvertebrae100,100ato thereby join thevertebrae100,100atogether.
• As previously indicated, end caps[0080]18,20 are preferably formed from high density polyethylene. Such material is nonabrasive and inert, and has a slippery touch. This latter feature is particularly valuable for trailingend cap20, which may oppose the epidural tissue. To avoid damage or irritation of the dura, the slippery, inert, nonabrasive polyurethane trailingend cap20 is provided. Trailingend cap20 is intended to coveraxial opening46 and retain the bone chips withinchamber24 while providing a nonabrasive and nonirritating surface opposing the epidura. Also, like leadingend cap18, trailingend cap20 prevents disk material from enteringchamber24.
• In a preferred embodiment, the end caps[0081]18,20 formed of polyethylene which is radiolucent. Radiolucent material permits X-rays to pass. Accordingly, withradiolucent end caps18,20, an attending physician can study the growth of bone withinchamber24 without the need for exploratory surgery.
• It will be appreciated that[0082]radiolucent end cap18,20, while desirable in a preferred embodiment, are not necessary to the practice of the full scope of the present invention. For example, the leadingend14 could taper completely as an integral portion of thesolid body12 as shown in FIG. 2A. In such an embodiment, thebody12′ assumes a more complete hollow bullet-shaped profile where the leadingedge14′ includes a sharp point15′ to better assist the insertion and advancement of thebody12′ into the intervertebral space.
• In FIGS. 12 and 12A, the[0083]implant10 is shown installed on the left side (from the patient's perspective) of the anterior-posterior axis, A-P. For a posterior approach as shown in FIG. 12, it is anticipated that twoprostheses10 will be used, with a second implant disposed on the right side of the anterior-posterior axis, A-P, and installed in a manner identical to that ofimplant10 on the left side. However, for ease of illustration, the right side implant is not shown installed. When installed, such prostheses would be positioned with the right and left prostheses being symmetrically disposed about axis A-P.
• D. Alternative Design[0084]
• FIGS. 3A and 4A show an alternative. The[0085]implant10′″ of the embodiment of FIGS. 3A and 4A is identical to that discussed above except as to the placement ofholes32′″. For ease of understanding the comparison betweenimplant10′″ andimplant10, the reader will note that FIGS. 3A and 4A are the same view ofimplant10′″ as FIGS. 3 and 4 are ofimplant10. Since the elements of theimplant10′″ shown in FIGS. 3A and 4A are the same (except as will be described) as those shown in FIGS. 3 and 4, all similar elements are numbered identically except for the addition of the triple prime (′″).
• Unlike[0086]implant10,implant10′″ does not haveholes32′″ circumferentially spaced aboutbody12′″. Instead, as best shown in FIG. 4A, holes32′″ are placed on diametrically opposed sides ofbody12′″.
• Upon insertion of the[0087]implant10′″, the surgeon positions theimplant10′″ withholes32′″ opposing the bone material of thevertebra bodies100,100a. As a result, nodisc material114 may enter intochamber24′″. This prevents possible interference of disc material with the bone fusion process.
• To assist a surgeon, indicia markings[0088]15′″ are placed onflange44′″. The markings15′″ are aligned with the axis ofholes32′″. The surgeon turnsbody12′″ into position until markings15′″ are aligned pointing tobodies100,100a. So positioned, the surgeon knows theholes32′″ are opposing bone and not disc material.
• E. Alternative Method and Apparatus for Anterior Approach.[0089]
• The foregoing description and illustration describe the insertion of an[0090]implant10 through a posterior approach. FIGS. 13 and 13A show an alternative embodiment of the invention for use in an anterior approach where abore102′ is formed from the front of the spine and axially aligned with the anterior-posterior axis, A-P. Since thebore102′ is formed from an anterior approach, the size restrictions of a posteriorly formed bore (namely, locations of nerves and blood vessels) are largely avoided. As a result, a large diameter bore102′ can be formed. A comparison of FIGS. 12A and 13A show the relative increase of bore diameter. This increase results in an enhanced surface area of exposed vertebra bone and an increased amount of graft material in an implant.
• The[0091]implant10″ shown in FIGS. 13 and 13A may be identical in proportional dimensions to that ofimplant10, only enlarged to be received within thelarger bore102′. However, theimplant10″ shown in FIGS. 13 and 13A differs from that shown in FIGS. 12 and 12A. Namely, theimplant10″ shown in FIGS. 13 and 13A does not include a tapered leading end. Instead, theentire implant body12″ is cylindrical-shaped to illustrate that, while a tapered leading end is preferred, it is not necessary to practice the teachings of the present invention.
• F. Further Alternative Embodiments.[0092]
• FIGS.[0093]15-25 illustrate yet a further embodiment of an implant for use in spinal stabilization. As shown in those figures, the implant120 (shown assembled in FIGS. 23 and 25) includes a body portion122 (shown in perspective in FIGS. 14 and 15) which is generally oval-shaped in cross section and formed from rigid, biocompatible material (preferably titanium). Thebody122 includes generallyflat side walls124,126 joined by upper and lower semi-cylindricalarcuate ribs128.Arcuate ribs128 are spaced apart to define a plurality of upper and lower semicirculararcuate openings130 which provide communication between ahollow interior132 ofbody122 and an exterior. Theribs128 define upper and lower walls of theimplant120 with thewalls having openings130 therethrough.
• [0094]Body122 extends from a leading oranterior end133, and a trailing orposterior end134.Anterior end133 has a centrally positionedcover plate136 which partially coversend132 but leaves upper and lower semi-circularaxial openings138 exposing interior132 throughend133.
• Shown best in FIG. 16,[0095]body122 is tapered at theleading end133, with theside walls124,126 tapering inwardly at an angle A₇of preferably 10° each. Also, the upper and lower planar of theribs128 are tapered inwardly as best shown in FIG. 22 at a preferred taper angles, A₈, of about 3°. The edges defined by the juncture ofwalls124,126,ribs128 and end133 are rounded to facilitate insertion ofimplant120 as will be described.
• The posterior end[0096]134 (shown in FIG. 14) has anaxial opening142 which communicates with thebody interior132. A pair of opposing retainingribs146 are shown partially extending from theside walls124,126 intoopening142. Aposterior end cap147 is provided with an arcuate,smooth cap149 sized to coverend134 andopening142.End cap147 has retainingclips148 selected to snap behindribs146 to thereby attachcap147 against end144.
• G. Method of Use of Alternative Embodiment.[0097]
• [0098]Implant120 is intended for use in a posterior approach with twoprostheses120 being inserted on opposite sides of the anterior-posterior axis of a vertebra. For ease of illustration, only one prosthetic device is shown inserted in FIGS.23-25.
• FIG. 24 shows a method for drilling the[0099]bore154 to receive the oval-shapedimplant120. As shown in FIG. 24, threecircular bores150,151,152 are drilled in vertical alignment in opposingvertebra bodies100′,100a′ andseparating disk114′. The three bores150,151,152 cooperate to form a generally oval-shapedbore154.
• [0100]Bore154 is sized to be slightly smaller than the dimensions ofbody122. The surgeon inserts the taperedleading end133 intobore154. With any suitable hammering mechanism, the surgeon then impacts on the uncappedposterior end134 to drive theimplant120 into thebore154 as shown in FIGS. 23 and 25. The tapers A₇and A₈(FIGS. 16 and 22) and the rounded corners on leadingend133 assist in the insertion.
• With the implant fully inserted, the surgeon fills the[0101]chamber132 with graft medium155 (again, preferably bone chips), the surgeon then installs thepolyethylene posterior cap147 to coverposterior end134 and provide a non-abrasive surface opposing the epidura.
• The[0102]implant120 of FIGS.14-25 greatly enhances the depth of insertion into opposingvertebrae100′,100a′ through a posterior approach. Namely, anoval bore154 can be formed having a height, H₂(see FIG. 24) equal to about three times the diameter ofbores102 described in previous embodiments. This added depth directly into the bone material of thevertebra body100′,100a′ increases the surface area available for grafting to thereby enhance the probability of a successful graft. Also, the increased depth into each of the vertebra bodies provides increased surface to prevent relative rotation of the opposingvertebrae100′,100a′ about the axis of the spine.
• The[0103]side walls124,126 of the implant do not have openings and, therefore prevent disk material from penetrating into the chamber and thereby interfering with the bone fusion. Theimplant120 is sized for the upper andlower openings133 to be located completely above and below, respectively, thedisk layer114′. Also,plate136 onend133 is sized to be about the thickness oflayer114′ (or slightly greater) to prevent disk material from entering theinterior132 ofimplant120.Openings138 are positioned to oppose only bone ofvertebra100′,100a′.
• H. Additional Alternative Embodiments[0104]
• FIGS.[0105]26-29 show additional alternative embodiments of the present invention. FIG. 26 shows animplant body312 extending from aleading end314 to a trailingend316. Theleading end314 has anaxial opening340 formed therethrough in communication with abody chamber324. The trailingend316 has anopening344 in communication withchamber324.
• A plurality of[0106]threads326 surround thebody312. Further, a plurality ofholes332 are formed through the body.
• As shown best in FIG. 27, the[0107]holes332 do not extend radially from the longitudinal axis X′-X′ of thebody312. Instead, theholes332 have their axes Y′-Y′ disposed radially offset from the longitudinal axis X′-X′. By reason of this structure, anenhanced cutting edge333 is formed which opposes bone as thebody312 is threaded between the opposing vertebrae. Thecutting edge333 chips away at the bond forcing bone chips to fall through theholes332 into thechamber324.
• Also shown in FIGS. 26 and 27, a[0108]central rib325 is provided withinchamber324.Rib325 adds structural integrity to thebody312. Also, as shown best in FIG. 27, a noncircular opening327 (in the preferred embodiment of FIG. 27, a triangular-shaped opening327) is provided. Opening327 may receive the tip of a turning tool (not shown but similar totool200 in FIG. 1) which may be inserted within opening327 to turn thebody312 as it is being threaded between opposing vertebrae. In FIGS. 28 and 29, abody412 is provide withthreads426. The embodiment of FIGS. 28 and 29 surrounds central chamber424. Arib425 is provided withinchamber442.Rib425 is provided with anoval opening427 which may receive an oval tool tip (not shown but serving the function oftool tip200 of FIG. 1). The use of anoval opening427 in FIG. 29 or atriangular opening327 in FIG. 27 provides assistance to a surgeon indicating directional alignment of thebody412 with a patient's vertebrae.
• In FIGS. 28 and 29, different-[0109]sized holes432 and532 are shown. Specifically, holes532 are provided on diametrically opposite sides ofimplant body412 and are axially aligned with the longitudinal dimension X″-X″ ofoval opening427. The axes between opposingholes532 defines an axial line Y″-Y″ which separates the body into a right and left half (when viewed in FIG. 29). On opposite sides of the line Y″-Y″, holes432 are provided which are smaller in diameter than holes532. Similar toholes332 in FIG. 27, holes432 are provided with their axes offset from the central axes X″-X″ of FIG. 29 in order to define cuttingedges433 at the intersection between theholes432 and thethreads426.
• The[0110]enlarged holes532 are provided to align with the opposing vertebrae such that theholes532 oppose the vertebrae after full insertion of thebody412. Accurate alignment is provided by the surgeon aligning the longitudinal dimension of oval427 (by operation of an insertion tool not shown) to be in alignment with the vertebrae. When so aligned, thelargest holes532 oppose the vertebrae bone to insure least resistance to bone growth through thebody412. When implanting thebody412, the surgeon will provide a bone slurry filling the implant and theholes432,532 and surrounding thebody412. Further, upon implanting thebody412, the bone from the vertebrae is chipped by cuttingedges433 intoholes432. As a result, a solid bone mass is provided through theholes432 intochamber442 and surrounding and penetrating theimplant body412.
• From the foregoing detailed description of the present invention, it has been shown how the invention has been attained in a preferred embodiment, including alternative embodiments. However, modifications and equivalents of these concepts are intended to be included within the scope of this invention.[0111]

Claims (6)

What is claimed is:

1. An implant for insertion into a bore formed between opposing vertebrae of a spine where said vertebrae are separated by a spacing, said implant comprising:

a rigid body having a leading end and a trailing end spaced apart by a longitudinal axis of said body;

said body comprising at least exposed threads disposed at least partially between said leading end and said trailing end, said threads selected to engage vertebra material and draw said body along a direction of said axis upon rotation of said body about said axis;

said body having a hollow, generally cylindrical shell with said threads disposed on an exterior surface of said shell;

said body having means defining a chamber disposed within said body and said body is provided with a rib disposed within said cylindrical shell;

said body having means defining at least one opening formed through said body in communication with said chamber and with said opening extending generally radially to said axis; and

said body sized to have a dimension generally transverse to said longitudinal dimension selected to be greater than said spacing for said body to urge said opposing vertebrae apart upon insertion of said body between said vertebrae with a portion of said body opposing a first of said opposing vertebrae and with an opposite side of said body opposing a second of said opposing vertebrae.

2. An implant for insertion into a bore formed between opposing vertebrae of a spine where said vertebrae are separated by a spacing, said implant comprising:

a rigid body having a leading end and a trailing end spaced apart by a longitudinal axis of said body;

said body comprising at least exposed threads disposed at least partially between said leading end and said trailing end, said threads selected to engage vertebra material and draw said body along a direction of said axis upon rotation of said body about said axis;

said body having a hollow, generally cylindrical shell with said threads disposed on an exterior surface of said shell;

said body having means defining a chamber disposed within said body;

said body having means defining at least one opening formed through said body in communication with said chamber and with said opening extending generally radially to said axis said opening comprising a hole formed through said shell with said hole disposed with an axis offset from said longitudinal axis; and

said body sized to have a dimension generally transverse to said longitudinal dimension selected to be greater than said spacing for said body to urge said opposing vertebrae apart upon insertion of said body between said vertebrae with a portion of said body opposing a first of said opposing vertebrae and with an opposite side of said body opposing a second of said opposing vertebrae.

3. An implant for insertion into a bore formed between opposing vertebrae of a spine where said vertebrae are separated by a spacing, said implant comprising:

a rigid body having a leading end and a trailing end spaced apart by a longitudinal axis of said body;

said body comprising at least exposed threads disposed at least partially between said leading end and said trailing end, said threads selected to engage vertebra material and draw said body along a direction of said axis upon rotation of said body about said axis;

said body having a hollow, generally cylindrical shell with said threads disposed on an exterior surface of said shell;

said body having means defining a chamber disposed within said body;

said body having means defining at least one opening formed through said body in communication with said chamber and with said opening extending generally radially to said axis;

said body sized to have a dimension generally transverse to said longitudinal dimension selected to be greater than said spacing for said body to urge said opposing vertebrae apart upon insertion of said body between said vertebrae with a portion of said body opposing a first of said opposing vertebrae and with an opposite side of said body opposing a second of said opposing vertebrae; and

indicator means for indicating an alignment of said body, said opening comprising holes formed through said shell and said holes including a first plurality disposed in alignment with said indicator and a second plurality disposed transverse to said indicator, said first plurality having openings sized greater than openings of said second plurality.

4. An implant for insertion into a bore formed between opposing vertebra of a spine, said implant comprising:

a rigid body having a leading end and a trailing end spaced apart by longitudinal axis of said body;

said body having exposed threads disposed at least partially between said leading end and said trailing end, said threads selected to engage a vertebra material and draw said body along a direction of said axis upon rotation of said body about said axis;

said body having means defining a chamber disposed within said body;

said body having a plurality of holes formed through said body in communication with said chamber, said holes disposed with a hole axis offset from said longitudinal axis.

5. An implant for insertion into a bore formed between opposing vertebra of a spine, said implant comprising:

a rigid body having a leading end and a trailing end spaced apart by a longitudinal axis of said body;

said body having exposed threads disposed at least partially between said leading end and said trailing end, said threads selected to engage a vertebra material and draw said body along a direction of said axis upon rotation of said body about said axis.

said body having means defining a chamber disposed within said body;

said body having means defining a plurality of holes formed through said body in communication with said chamber;

indicator means for indicating an alignment of said body with respect to said vertebra; and

said holes including at least a first plurality disposed in alignment with said indicator and a second plurality disposed out of alignment with said indicator.

6. An implant according toclaim 5 wherein said first plurality have opening size greater than openings of said second plurality.

Images